OPTICAL PROPERTIES OF THE OXIDATION OF Cu THIN FILMS PREPARED BY THERMAL EVAPORATION

Abstract

Copper films with 87 nm thickness were deposited on quartz substrates by thermal evaporation. In order to investigate the oxidation process, the Cu films were oxidized at different temperatures in air with different durations to obtain the complete and uncompleted copper oxide films. The structure and optical properties of the samples were studied by X-ray diffraction, scanning electron microscopy and spectrophotometer, respectively. It is found that the sample oxidized at 220°C for 200 min is Cu2O film with 106 nm thickness. Both the transmittance and reflectance of the samples increase with the increase of oxidation duration. The optical constants of the Cu film and the Cu2O film were retrieved by simulating the reflectance or transmittance based on the optical dielectric models. The optical constants of the Cu and Cu2O mixed layer with different composition were calculated by the effective medium theories. Adjusting the mixed layers composition and thickness, and Cu2O layer thickness, the transmittance and reflectance of the uncompleted oxidation films were simulated by optical multilayer design software. The results show that the uncompleted oxidation films consist of the Cu and Cu2O mixed layers and Cu2O layer. According to the parabolic rate law, the increase rate of Cu2O layer thickness for the uncompleted oxide films at 200°C is 1.6 nm s-1/2.